This invention relates to an encapsulated high voltage switching device such as a vacuum fault interrupter having a movable contact rod in sliding contact with a high voltage contact and terminal assembly.
In residential power distribution systems and the like, circuit interrupters are incorporated into the system to provide automatic protection in response to abnormal load or line conditions and to permit manual opening and closing of the circuit. The interrupters may advantageously seal the contacts in a vacuum enclosure with a movable contact having an operating contact rod extending through a vacuum seal in one end of the enclosure. A particularly satisfactory encapsulated interrupter is disclosed in the copending application of Kumbera et al, entitled "PROTECTIVE SWITCH DEVICE AND OPERATING MECHANISM THEREFOR," filed on Mar. 6, 1975, with Ser. No. 555,948, and assigned to the same assignee as this application. As more fully disclosed therein, the vacuum interrupter advantageously includes an outer solid, thick insulating wall or shell case in intimate contact with the vacuum enclosure to form a self-supporting unit within which a fixed contact assembly and a movable contact assembly are disposed. High voltage current exchange assemblies are provided for connecting of the contact assemblies in circuit. The movable contact includes an operating rod or shaft projecting outwardly of the encapsulating insulating wall and sliding through a pair of circuit contact springs in the high voltage current exchange assembly which are case into the shell to maintain an integral outer wall member with the single opening from which the movable contact extends in a sealed manner.
The current exchange assemblies are specially formed to distribute or grade the high voltages in the connection and essentially eliminate high stress of the insulation. As disclosed in the above-entitled application, an operating guide member of suitable insulating material preferably lines the rod opening to extend concentrically of the operating member and functions to prevent high voltage tracking along such opening. A conductive layer may also be provided extending along the outer surface of the guide tube from the current exchange assembly to distribute the field and prevent high stress on the insulation.
Although the encapsulated vacuum fault interrupter has been found to provide a highly reliable, lightweight fault interrupter having a long life and minimum service requirements, recent demands for still higher impulse voltage ratings require further improvement in the termination or connection capability, particularly in the sliding connection of the movable contact.